1. Field of the Invention
This invention relates generally to electrical computers and data processing systems particularly printing systems providing varied spacing between the centers of alpha-numeric characters in proporation to the widths of the characters and, more particularly, to such a printing system further incorporating a tabbing function.
2. Description of the Prior Art
Printing systems comprise a printer and electronic circuitry for the control of the printer. A printer may be constructed in a variety of forms such as a flying spot scanner in television-type displays, laser beam scanning by multifaceted rotating mirrors upon a photosensitive medium, and electrical excitation of a stylus upon an electrophoretic medium. The electronic control circuitry includes some form of character generator with scanning and position control units.
In the design of such systems, consideration is given to the spacing between centers of the alpha-numeric characters which are to be printed on a screen or on hard copy such as paper. When thus spacing is equal, in which case all characters are allotted the same cell size, wide characters appear to be more closely spaced than narrow characters. In order to present a more pleasing appearance to the printed text, proportional width printing has been introduced to provide a variation in the cell size allocated to each character in proportion to the width of the character. A uniform spacing is thereby maintained between the leading and trailing edges of each cell and, correspondingly, between each character for a more pleasing uniformity to the text.
However, a problem arises with proportional width printing in the case of presenting data in columnar fashion. The problem is most readily understood with reference to the construction of the printing system. In order to provide for the proportional width printing, the character generator must signal the conclusion of the printing of a character before the printing of the next character can be commenced. Such a signal is designated as an end of character (EOC) flag. Upon each occurrence of the EOC flag, the instruction for the next character is transmitted to the character generator.
However, in a columnar presentation as appears in newspaper-like format, such as that having two or more columns of text information side-by-side on a page, the leading edges of the characters along the left margin of each column are to be aligned with a vertical line. Thus, the positioning of a character is no longer keyed to the end of a previous character, but is keyed to the location of the column. In order to determine the starting point of a character in such columnar presentation, it has been the practice to utilize a computer within the printing system to calculate the amount of space required between two successive characters based on the spacing between the last character in a print line of a column and the first character in the same print line of the next column.
The foregoing illustrates limitations of the known prior art. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations as set forth above. Accordingly, a suitable alternative is to provide a printing system including the functions of both the proportional width and the columnar presentation without the necessity of the foregoing calculations.